To ensure safety and to provide a comfortable driving experience, automotive disc brake systems must operate smoothly and predictably. However, when disc brake system components do not meet tolerances or become damaged through use, the driver of a vehicle may experience uncomfortable sensations such as brake judder, steering wheel shimmy or vehicle body vibration, and performance of the disc brake system may be compromised. Accordingly, initial quality control of brake system components and subsequent maintenance of those components are crucial to providing a safe and comfortable driving experience.
Conventional disc brake systems for vehicles include a hardened metal brake rotor that rotates with a wheel of the vehicle and a pair of high-friction brake pads that are fixed with respect to the vehicle such that they do not rotate with the wheel. In order to slow the vehicle, the brake pads are disposed on opposite sides of the rotor, and are brought into engagement with the rotor by a caliper.
Brake rotor abnormalities are a significant source of disc brake system problems. The two primary brake rotor abnormalities are run out and thickness variation. Run out refers to the amount by which the surface of the brake rotor deviates from a single plane perpendicular to the axis of rotation of the wheel when the brake rotor is rotated. Thickness variation refers to the amount by which the distance between opposite sides of the brake rotor varies at different locations on the brake rotor.
Conventionally, brake rotor run out measurements are made using a linear displacement measurement tool, such as a dial gauge. One known run out measuring method includes the steps of placing the vehicle on a lift and removing the wheel of the vehicle corresponding to the brake rotor to be measured. The technician performing the measurement places the dial gauge into engagement with a first side of the brake rotor, for example, by supporting the dial gauge with respect to the vehicle using an adjustable support arm that magnetically attaches to a portion of the vehicle. The technician then records measurements at discrete locations on the brake rotor while rotating the brake rotor slightly in between measurements, until measurements have been recorded for a full rotation of the brake rotor. After the run out of the first side of the brake rotor is measured, the dial gauge is repositioned so that it engages a second side of the brake rotor, and the process is repeated. Thickness variation is measured at numerous locations on the brake rotor using a micrometer while the vehicle is on the lift and the wheel is removed.
The above-described testing procedure has been previously refined by using a pair of electronic sensors that measure both sides of the brake rotor at once and automatically output measurements to a data recording device, such as a portable computer. This refined measuring method includes the steps of placing the vehicle on a lift and removing the wheel of the vehicle corresponding to the brake rotor to be measured. In addition, the brake caliper and the caliper mounting bracket are removed to provide clearance for a sensor mounting bracket. The brake rotor is then rotated, and the sensors transmit data regarding the surface characteristics of the brake rotor to the computer. Since sensors are placed on both sides of the brake rotor, run out and thickness are measured simultaneously.
While conventional brake rotor testing methods provide accurate run out and thickness measurements, they are time consuming, due to the need to remove the wheel and, in some methods, due to the need to remove the brake caliper and the brake caliper mounting bracket. It would be desirable to provide a method and apparatus for testing a brake rotor that could provide accurate run out and thickness measurements without removing the wheel or brake caliper from the vehicle.